"Nun too Fast" joke

A police officer pulled over a nun driving a car, and said,' Ma'am, you're driving too slow, could you please drive faster?"

And the nun says,' Oh, I saw the sign with the "21" and assumed the speed limit was 21."

The officer explains:' No ma'am, the speed limit is 65, the highway is 21."

Then the police officer looks in the back and see the other 2 nuns shaking like leaves.

"Excuse me, Sister, but what's wrong with those 2?"

"Oh, that's because we just got off Highway 145."